A. Field of the Invention
The present invention relates generally to the field of voltage regulators and variable voltage sources and more particularly to an AC variable voltage source utilizing pulse width modulation techniques to provide a continuously variable AC voltage in response to an AC voltage input.
B. Description of the Prior Art
Various power supplies, regulators, inverters and converters are known that utilize various techniques such as phase control, pulse width modulation, switching of winding taps, and saturable coils for obtaining regulated supply voltages at various levels.
For example, switching regulators of one type utilize pulse width modulation of a series switching device to provide control of an average power output. This type of switching regulator is typically a DC to DC regulator. However, AC to AC converters are also known wherein the AC input voltage is rectified, an intermediate DC control stage with pulse width modulation control or other switching control is utilized to regulate the rectified AC input voltage, and a DC to AC inverter stage is provided to convert the regulated DC voltage to an AC output.
Further, various buck and boost regulators and other arrangements are known which provide line regulation and control of output voltage by automatically switching taps on transformer windings by discrete steps to provide a measure of output control in response to variable input conditions.
Another form of voltage regulation control is achieved by arrangements utilizing saturable ferromagnetic transformers or variable inductance devices to provide output control.
While the above-described arrangements and techniques are generally suitable for their intended use, the various arrangements suffer from various drawbacks in that they are inefficient, or merely control the output voltage in discrete steps, or require AC to DC to AC conversion with synthesis of the AC output waveform.